I now have a "19T" Yam. black prop. Its 19 pitch by 13 1/2 diam (rough measured) . Yam's website says that with a 15 1/4 x 17 SWS I should get 6000 rpm @ 42 mph, with the sweet spot achieving 3.27 m.p.g. Right now I get 5300 rpm @ 35 mph (1 person no gear). If i went from a 19 to a 17 wouldn't I lose m.p.h. ? I'm sure someone here has figured out the best prop for that boat. I don't want to blow $500.00 for a prop thats wrong. By the way is a Yam. SWS worth the extra $$ or is only the pitch & diam. important ? Thanks !!